1. Field of the Invention
The invention relates in general to a pulse width (PW) digitizer, and more particularly to a PW digitizer incorporating delta-sigma modulation.
2. Description of the Related Art
Nowadays, pulse width (PW) signal modulation and detection has been well-known and been applied in a great variety of aspects. Generally, how to detect the PW with fine resolution is a prominent object of the related industry. Conventionally, various methods, such as low-pass filter method and direct-sampling method, exist for PW detection. The low-pass filtering method employs PW signals having the pulse-width information in voltage domain. The PW signal is first averaged by a low pass filter to extract a direct current (DC) voltage. Then the DC voltage is compared by a voltage comparator with a threshold voltage. However, the smoothness of low-pass-filtered pulse signal affects the resolution of pulse-width detection, which can be achieved by extracted over many quench periods, resulting in a trade-off between resolution and conversion speed.
The direct-sampling method, on the other hand, processes the data in time domain. The PW signal is firstly hard limited, and then is directly sampled by a high frequency reference clock to achieve the PW detection. However, the resolution of the pulse-width detection is severely limited by time-domain quantization noise due to insufficient sampling frequency (i.e., quantization jitter) and the quantization jitter due to insufficient sampling frequency is still the dominant resolution limitation in this method.
Thus, how to find a method capable of solving the up-mentioned problems of the known PW signal modulation and detection methods and detecting the PW with fine resolution is a prominent goal for the industries.